Add ability for debugfs to use a separate source of data blocks when
reading from an e2image file.  (New -d option)

Add new functions ext2fs_get_data_io, ext2fs_set_data_io,
ext2fs_rewrite_to_io to libext2fs library.

diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
index 74f20a7..2ee06b5 100644
--- a/lib/ext2fs/initialize.c
+++ b/lib/ext2fs/initialize.c
@@ -91,6 +91,7 @@
 	retval = manager->open(name, IO_FLAG_RW, &fs->io);
 	if (retval)
 		goto cleanup;
+	fs->image_io = fs->io;
 	fs->io->app_data = fs;
 	retval = ext2fs_get_mem(strlen(name)+1, &fs->device_name);
 	if (retval)